The present invention relates to an oxide sintered compact, an oxide sputtering target, and an oxide thin film, and in particular relates to an oxide sputtering target which can be used in DC sputtering, and an optical adjustment oxide thin film having a low refractive index and high transmissivity produced from the foregoing oxide sputtering target.
When using visible light in various optical devices such as organic EL, liquid crystal displays and touch panels, the used material must be transparent, and in particular desirably yields high transmissivity in the entire visible light region. Moreover, with various optical devices, there are cases where optical loss arises due to a refractive index difference at the interface with the constituent film material or the substrate. In order to achieve high transmissivity, reduction in optical loss, and antireflection, there is a method of introducing an optical adjustment layer (film).
As the optical adjustment layer, films of high refractive index, medium refractive index, and low refractive index are being used as a single layer or as laminated layers according to the device structure and usage thereof (Patent Documents 1 to 3, etc.). While there are various methods for depositing this kind of optical adjustment layer, deposition via the sputtering method is especially superior as a uniform deposition means on a large area. Meanwhile, when depositing a film having a low refractive index via sputtering, there are problems in that DC sputtering cannot be adopted and the deposition rate is slow since many of the low refractive index materials (for example, SiO2, MgO, and Al2O3) possess insulation properties.
In order to deal with the foregoing problem, there is a method of increasing the deposition rate by subjecting a metal target to reactive sputtering in an oxygen atmosphere. Nevertheless, when a device structure needs to use an oxygen-averse layer such as a metal film or an organic film, there is a problem in that sputtering cannot be performed in an oxygen atmosphere. Accordingly, particularly in cases of forming a film having a low refractive index, there are problems in that high-speed deposition via DC sputtering cannot be performed and the productivity is inferior.
Generally speaking, as transparent materials, IZO (indium oxide-zinc oxide), GZO (gallium oxide-zinc oxide), AZO (aluminum oxide-zinc oxide) and the like are known. For example, Patent Document 4 discloses a zinc oxide sintered compact and its production method, and Patent Documents 5 and 6 disclose a sputtering target for forming a transparent oxide film containing Al, Ga, and Si, and the remainder being Zn and unavoidable impurities.
Moreover, Patent Document 7 discloses a Zn—Si—O-based oxide sintered compact containing zinc oxide as its primary component and additionally containing Si, and to which one type of element selected from Mg, Al, Ti, Ga, In and Sn is added. Nevertheless, as described above, since a target containing a low refractive index material having a refractive index of 1.8 or less has high insulation properties, there are problems in that, depending on the composition, DC sputtering cannot be performed and the deposition rate is slow.